/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jakarta.servlet.jsp.tagext;

import java.io.IOException;

import jakarta.servlet.jsp.JspContext;
import jakarta.servlet.jsp.JspException;
import jakarta.servlet.jsp.SkipPageException;

/**
 * Interface for defining Simple Tag Handlers.
 * <p>
 * Simple Tag Handlers differ from Classic Tag Handlers in that instead of supporting <code>doStartTag()</code> and
 * <code>doEndTag()</code>, the <code>SimpleTag</code> interface provides a simple <code>doTag()</code> method, which is
 * called once and only once for any given tag invocation. All tag logic, iteration, body evaluations, etc. are to be
 * performed in this single method. Thus, simple tag handlers have the equivalent power of <code>BodyTag</code>, but
 * with a much simpler lifecycle and interface.
 * </p>
 * <p>
 * To support body content, the <code>setJspBody()</code> method is provided. The container invokes the
 * <code>setJspBody()</code> method with a <code>JspFragment</code> object encapsulating the body of the tag. The tag
 * handler implementation can call <code>invoke()</code> on that fragment to evaluate the body as many times as it
 * needs.
 * </p>
 * <p>
 * A SimpleTag handler must have a public no-args constructor. Most SimpleTag handlers should extend SimpleTagSupport.
 * </p>
 * <p>
 * <b>Lifecycle</b>
 * </p>
 * <p>
 * The following is a non-normative, brief overview of the SimpleTag lifecycle. Refer to the JSP Specification for
 * details.
 * </p>
 * <ol>
 * <li>A new tag handler instance is created each time by the container by calling the provided zero-args constructor.
 * Unlike classic tag handlers, simple tag handlers are never cached and reused by the JSP container.</li>
 * <li>The <code>setJspContext()</code> and <code>setParent()</code> methods are called by the container. The
 * <code>setParent()</code> method is only called if the element is nested within another tag invocation.</li>
 * <li>The setters for each attribute defined for this tag are called by the container.</li>
 * <li>If a body exists, the <code>setJspBody()</code> method is called by the container to set the body of this tag, as
 * a <code>JspFragment</code>. If the action element is empty in the page, this method is not called at all.</li>
 * <li>The <code>doTag()</code> method is called by the container. All tag logic, iteration, body evaluations, etc.
 * occur in this method.</li>
 * <li>The <code>doTag()</code> method returns and all variables are synchronized.</li>
 * </ol>
 *
 * @see SimpleTagSupport
 *
 * @since JSP 2.0
 */
public interface SimpleTag extends JspTag {

    /**
     * Called by the container to invoke this tag. The implementation of this method is provided by the tag library
     * developer, and handles all tag processing, body iteration, etc.
     * <p>
     * The JSP container will resynchronize any AT_BEGIN and AT_END variables (defined by the associated tag file,
     * TagExtraInfo, or TLD) after the invocation of doTag().
     *
     * @throws JspException      If an error occurred while processing this tag.
     * @throws SkipPageException If the page that (either directly or indirectly) invoked this tag is to cease
     *                               evaluation. A Simple Tag Handler generated from a tag file must throw this
     *                               exception if an invoked Classic Tag Handler returned SKIP_PAGE or if an invoked
     *                               Simple Tag Handler threw SkipPageException or if an invoked Jsp Fragment threw a
     *                               SkipPageException.
     * @throws IOException       If there was an error writing to the output stream.
     */
    void doTag() throws JspException, IOException;

    /**
     * Sets the parent of this tag, for collaboration purposes.
     * <p>
     * The container invokes this method only if this tag invocation is nested within another tag invocation.
     *
     * @param parent the tag that encloses this tag
     */
    void setParent(JspTag parent);

    /**
     * Returns the parent of this tag, for collaboration purposes.
     *
     * @return the parent of this tag
     */
    JspTag getParent();

    /**
     * Called by the container to provide this tag handler with the <code>JspContext</code> for this invocation. An
     * implementation should save this value.
     *
     * @param pc the page context for this invocation
     *
     * @see Tag#setPageContext
     */
    void setJspContext(JspContext pc);

    /**
     * Provides the body of this tag as a JspFragment object, able to be invoked zero or more times by the tag handler.
     * <p>
     * This method is invoked by the JSP page implementation object prior to <code>doTag()</code>. If the action element
     * is empty in the page, this method is not called at all.
     *
     * @param jspBody The fragment encapsulating the body of this tag.
     */
    void setJspBody(JspFragment jspBody);
}
